Topic 12: Intracellular Compartments and Protein Sorting Part 1
These synthesize proteins that are simultaneously transferred into the ER
What are Membrane-bound ribosomes?
The ER membrane is the site of synthesis of nearly all of the cell’s major classes of lipids including phospholipids and cholesterol that are major components of the cell membrane. The major phospholipid phosphatidylcholine is formed in three steps from choline, two fatty acids, and glycerol phosphate.
What are the three components of phosphatidylcholine?
Transport vesicles continually bud off from one membrane compartment and fuse with another, carrying membrane components and soluble lumenal molecules. These membrane components and soluble molecules are called cargo proteins.
What are cargo proteins?
This cellular compartment makes up 50% of the cell
What is the cytosol?
This catalyzes the oxidation of free sulfhydryl groups on cysteines to form disulfide bonds
What is a PDI (Protein Disulfide Isomerase)?
In the ER, phospholipids equilibrate across the membrane within minutes. This rapid movement between two monolayers of the cell membrane is mediated by phospholipid translocator scramblase. It non-selectively equilibrates phospholipids between the two leaflets of the lipid bilayer.
What is the role of scramblase?
SNARE proteins are members of a large family of transmembrane proteins present in organelle membranes and the vesicles derived from them. SNAREs catalyze many membrane fusion events in cells. They exist in pairs—a v-SNARE in the vesicle membrane that binds specifically to a complementary t-SNARE in the target membrane.
What are SNARE proteins?
This type of transcriptional regulatory protein will turn off a gene that is already activate.
What is a repressor?
This chaperone protein will bind to a polypeptide chain as it emerges from the Sec61 complex pore. This protein, once bound, will prevent backsliding of the nascent chain. It can also be recycled through the process of ATP hydrolysis
What is BiP?
Ceramide is a sphingolipid produced in ER by first condensing amino acid serine to a fatty acid to form amino alcohol sphingosine and in second step another fatty acid is covalently added. Ceramide is exported to golgi apparatus where it serves as a precursor for generating glycophospholipids and sphingomyelin.
What is the precursor for glycophospholipids and sphingomyelin?
There are four well-characterized types of coated vesicles, distinguished by their major coat proteins: clathrin-coated, COPI-coated, COPII-coated, and retromer-coated. Each type is used for different transport steps
What are the 4 types of coated vesicles?
Once N-linked oligosaccharide has been added to the protein, glucosidases remove two of the three glucoses. __ and __ bind to the N-linked oligosaccharides and help the protein fold
What are calnexin and calreticulin?
In N-linked glycosylation, this enzyme catalyzes a transfer of an oligosaccharide from a lipid molecule (dolichol) to a protein with a N-glycosylation site
What is oligosaccharyl transferase?
In eukaryotic cells, peroxisomes are small membrane-bounded organelle that uses molecular oxygen to oxidize organic molecules. They contain one or more enzymes that use molecular oxygen to remove hydrogen atoms from specific organic substrates in an oxidation reaction that produces hydrogen peroxide, H2O2.
What are peroxisomes?
Clathrin is a protein that assembles into a polyhedral cage on the cytosolic side of a membrane so as to form a clathrin-coated pit, which buds off by endocytosis to form an intracellular clathrin-coated vesicle. Clathrin-coated vesicles mediate transport originating from the Golgi apparatus, endosome, and the plasma membrane.
what is the role of clathrin coated vesicles?
Cells need to respond to environmental cues and responses might be different between cell types. mRNA levels for Tyrosine aminotransferase (TAT) _1_ in hepatocytes in response to high glucocorticoids levels while mRNA levels _2_ in adipocytes.
What is 1) increase and 2) decrease?
In unfolded protein response, this kinase oligomerizes and auto-phosphorylates an endoribonuclease domain on its cytosolic side. This domain then cleaves a specific RNA molecule, removing an intron to create a mRNA. This molecule is then translated into a transcription regulator which enters the nucleus and triggers the transcription of ER chaperones. These chaperones enter the ER and help fold proteins
What is IRE1?
TIM complexes are a groups of protein translocators in the mitochondrial inner membrane that moves proteins and some non-coding RNA across the membrane: The TIM23 complex mediates the transport of proteins into the matrix and the insertion of some proteins into the inner membrane; the TIM22 complex mediates the insertion of a subgroup of proteins into the inner membrane.
What are TIM protein complexes?
Trans Golgi network (TGN) is a network of interconnected tubular and cisternal structures closely associated with the trans face of the Golgi apparatus and the compartment from which proteins and lipids exit the Golgi, bound for the cell surface or another compartment.
What is trans Golgi network?
In a helix turn helix structural motif, this term describes the more C terminal helix, which fits into the major groove of DNA and has a sequence specific to that binding location.
What is the recognition helix?